[Bug middle-end/95848] missing -Wuninitialized passing structs by value (VOPS)

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95848

--- Comment #4 from Martin Sebor <msebor at gcc dot gnu.org> ---
There's no code code to handle the last case.  The first case is handled
because the local s is assigned to a temporary and there is code to detect
uninitialized sources of assignments.  The second case is handled in the new 
maybe_warn_pass_by_reference() function.  The third case enters the function
but is excluded because the argument is passed by value and nothing else checks
passing non-SSA_NAME operands.

In the test case below passing the uninitialized i is diagnosed because i's an
SSA_NAME.  Passing s isn't because it's not one. 
maybe_warn_pass_by_reference() should handle this case as well (and be renamed
appropriately).

$ gcc -S -Wall -fdump-tree-ssa=/dev/stdout ../t.c

;; Function h (h, funcdef_no=0, decl_uid=1948, cgraph_uid=1, symbol_order=0)

void h ()
{
  int i;
  struct S s;

  <bb 2> :
  fs (s, i_2(D));
  s ={v} {CLOBBER};
  return;

}


../t.c: In function ‘h’:
../t.c:9:3: warning: ‘i’ is used uninitialized [-Wuninitialized]
    9 |   fs (s, i);
      |   ^~~~~~~~~